The present invention is concerned with semiconductor device manufacturing equipment, and is more particularly concerned with arrangements for securely holding a substrate while rotating the substrate.
Semiconductor device manufacturing generally entails performing a number of processes with respect to a substrate such as a silicon wafer to form integrated circuits on the substrate. For some of the processes, it is necessary or desirable to hold a substrate in a horizontal position while rotating the substrate. For this purpose, it is known to provide a rotary vacuum-chuck which holds the substrate horizontally on a chuck surface while rotating the substrate. In one conventional rotary vacuum-chuck, a chuck surface is mounted on a hollow rotary shaft that is coupled to a vacuum generator. The hollow rotary shaft, in turn, is mounted on a rotary junction or xe2x80x9cunionxe2x80x9d that includes a seal to maintain vacuum within the rotary shaft. A conventional seal may include a rotary disk that rotates with the rotary shaft and a confronting, stationary disk against which the rotary disk rubs.
Problems encountered with conventional seals for rotary vacuum-chucks include a limited useful life due to wear of the seal, and a tendency to generate particles that may contaminate the substrate that is being processed (e.g., as the rotary disk and stationary disk rub together). Further, conventional seals require the rotary shaft to be driven with an additional torque to overcome the frictional forces between the rotary and stationary disks of such seals. Conventional seals also tend to generate heat, and may limit the rotational velocity at which it is practical to rotate a substrate.
Another conventional rotary union known as a xe2x80x9ccontrolled gapxe2x80x9d rotary union maintains a small gap (e.g., 5-15 xcexcm over 50-100 mm of engagement) between stationary and rotating parts. A problem with this type of rotary union is the expense of machining the parts, and the tendency for particles to collect in the small, controlled gap. Such particle accumulation may interfere with rotation.
According to a first aspect of the invention, a rotary vacuum-chuck adapted to hold a substrate for rotation is provided. The vacuum-chuck according to this aspect of the invention includes a hollow rotary shaft having a chuck with a surface adapted to support a substrate. The surface has one or more openings in fluid communication with the hollow rotary shaft. A venturi is positioned adjacent a first end of the hollow rotary shaft, and an inlet is adapted to couple to a source of gas and to direct a flow of gas through the venturi so as to evacuate the hollow rotary shaft and the one or more openings in the surface of the chuck. As used herein a venturi is adjacent an end of a hollow rotary shaft if the venturi is close enough to the end of the hollow rotary shaft to generate a desired vacuum level within the hollow rotary shaft (e.g., a vacuum level that is sufficient to hold a substrate against the chuck as the hollow rotary shaft is rotated at a desired speed).
With the rotary vacuum-chuck of the present invention, seals that employ rubbing parts may be eliminated, so that the generation of potentially contaminating particles may be reduced. Moreover, the maintenance burden that may otherwise occur in connection with periodic replacements of a seal may be avoided; and the rotational speed at which the vacuum-chuck may rotate is not limited by the friction between rubbing portions of a seal. In one aspect, the generation of vacuum at an end of the hollow rotary shaft provides for efficient coupling of vacuum to the rotary shaft and the chuck surface. In a further aspect, the present invention allows for a relatively large gap to exist between the stationary and rotating parts of the rotary vacuum-chuck while still generating a desired vacuum at the chuck surface.
Other features and advantages of the present invention will become more fully apparent from the following detailed description of exemplary embodiments, the appended claims and the accompanying drawing.